This is a potentially large topic and one which I have a particular interest in thinking more on. So I've moved it over from the other thread. Please share in my thinking-out-loud here:MSimon wrote:But is it a "real" discharge event? The current is limited by well formation.chrismb wrote:The difference isn;t the issue, the mix is. Magentrons have no ions in them, just a load of space-charge inducing electrons. This is something quite different to a thyratron with a 'quasi-neutral' mix of ions and electrons undergoing a discharge event.MSimon wrote:chris,
Other than the mass difference why should ions vs electrons matter?
Some times you seem so perceptive and other times you seem thicker than a brick. It is like two different people using your name.
And well formation says that there may be a series of layers of alternating separated charges.
Of course with no data to go on you could be right. OTOH we have the Navy puttying up significant money so the odds are that something so fundamental is not a problem.
Most controlled fusion attempts to date are by some form of plasma discharge, which seems very very wasteful to me as what ends up happening is that the electrons suck up all the energy for themselves (greedy little blighters!) then radiate it indulgently whilst they play amongst themselves. Chucking a big current through a gas/plasma can certainly accelerate particles within it but they are poorly directed and thermalise essentially instantly, so you've gotta heat the whole lot up in one go as you can't get the energy into a targeted number of particles. Not wanting to draw too strong a conclusion, but it is of no surprise to my thinking that the only known over-unity fusion reactions (natural or man-made) do not involve electrical discharges.
It is also, then, of no surprise in this line of thinking that the way forward needed with Tokamak is to remove the dependency on the toroidal current. The approach is to cause to generate so called 'banana' orbits that will use thermal motion to generate the necessary particle currents, i.e., that will mean it is no longer a discharge device (by virtue of it being simply the 'shorted secondary' of a huge transformer).
(In that context, perhaps the stellarators (that do not depend on that induction current) have an immediate advantage over tokamkas, but simply they've been too complex to build until more powerful computers have been able to help design the required magnetic coils. Nonetheless, I think the biggest SC version of this, LHD, has maintained a fusion-type plasma for the longest period so far.)
So we turn to Polywell; will it run as a discharge device, or will it act as something else? There are other types of ion generating devices that do not rely on electrical discharge and produce and retain ions in the, arguably, most efficient way possible. These are crossed-field devices like the Penning trap, the Hall effect thruster and 'anode layer' ion source, all of which work in very similar ways. They have no such losses as discharge devices and might theoretically draw no current whatsoever to maintain what is then a non-neutral population of particles (were ions and electrons not prone to gyro-orbit hop across the magnetic field).
Sound similar to Polywell? It does have commonality with some of the features of these devices, but I also can see the potential for a large amount of discharge current being pulled by the device (through the electron guns) because it is not a well-defined ExB volume, only that it is so in the uniform bits away from the cusps, as evidenced by the well-discussed electron losses.
So I'm thinking that I generally judge a fusion device by its input current, as a first-pass towards considering any viability. How much external discharge current does the Sun pull – none, so it's 'got a chance of working' (!). How much external discharge current does an H-bomb pull – none, so 'that might work' as well!! How much does a tokamak draw – multi mega-amps. How much does a fusor draw – 10's mA, but that's quite a bit considering the relatively small population of ions it actually gets, and keeps, moving.
How much does the Polywell suck up? This will be one measure I judge it by.
So in reply to MSimon, I agree it will not be an all-out discharge device, but nor will it be of the quality of efficiency of a 'non-discharge' Penning trap-type device.
(PS. I take the analogy that I am sometimes like a thick brick as a complement. Ask a guy in a hurricane with an ingeniously made paper house if he thinks a thick brick house has any particular benefits! My thick-brick status suggests a solid and stubborn contempt for conventionally accepted axioms – I like that you recognise this in me! But that's no licence to go too far with the ad hominem comments.)